A TECHNICAL SEMINAR ON

CRYOGENIC COOLING

INTRODUCTION

The word “cryogenics” is derived from two Latin words.

Cryo - means cold Genics - means science.

Cryogenics is “the science of cold”. It suggests that how to get low temperatures and how materials behave at the low temperatures

Cryogenic cooling or cryogenic refrigeration system is one of the system from cryogenic.This field has been an enormous growth especially after World War – II. To consider the field of cryogenics as that involving temperatures below 123K.

Refrigerants Boiling point

(K)

Liquid Helium 3 3.19

Liquid Helium 4 4.214

Liquid Hydrogen 20.27

Liquid Neon 27.09

Liquid Nitrogen 77.36

Liquid Air 78.8

CRYOGENIC REFRIGERATION SYSTEM: REFRIGERANTS

IDEAL REFRIGERATION SYSTEMS:-. In the case of refrigerators, there are two types of low-temperature source that may be used. If we evaporate a liquid to furnish the cooling, energy is added to the refrigerant in an isothermal manner, as far as the evaporator of the refrigerator is concerned. On the other hand, we may use a cold gas such as helium (which gets quite cold before it liquefies), and energy is added at constant pressure (for the refrigerant) without liquefying the gas.

T = const.

T = const.

s =

cons

t.

s =

cons

t.

12

3 4

Th

Tc

Entropy s

Tem

pera

ture

T

Fig. 1 Carnot cycle

3. REFRIGERATOR:- Linde- Hampson refrigerator:-

Magnetic Cooling: By using liquid He3 we can reach upto 0.6 K

by reducing pressure upto 72.6 Pa which is vapour pressure of He3. But it is difficult to maintain such low pressure.

Giauque and Debye pointed out that a paramagnetic substance could be used instead of a gas or liquid and that a magnetic field could be used instead of a fluid to attain the low temperatures.

CRYOGENIC COOLING BY OPEN SYSTEM In this method cryogenic cooling system use

an open system that expels the spent vapour into the atmosphere.

Cryogenic Cooling by open system

TYPICAL MECHANICAL COOLING SYSTEM

Advantage over mechanical cooling:

Change rates, or temperatures beyond the limits of mechanical refrigeration.

Small &lighter equipment requires less space.

less electrical power required due to absence of compressor.

less noise.lower maintenance cost.

Coolants: 1. Liquid CO2

2. Liquid N2

How safe is this system? Common cryogenic coolants do not harm the

Ozone layer, are not flammable, and are not poisonous. The common coolants, Carbon Dioxide and Nitrogen, are normal components of our breathable air. In fact, about 78% of our atmosphere is Nitrogen, so it’s safety is pretty well demonstrated. Carbon Dioxide is the fizzy part of soft drinks, so it better safe.

APPLICATIONS OF CRYOGENIC COOLING: In Space Research In Electronics In Biological & Medical applicationsIn Manufacturing ProcessIn Food Processing

References :- Cryogenic Systems by Randall Barron Refrigeration & Air conditioning by Arora,

Domkundwar www.sigmabroucher.com

THANKS